Printed circuit boards are often processed by transporting them through a series of processing chambers. Each chamber is adapted to perform one or more functions including: developing, etching, stripping, cleaning, and rinsing the printed circuit boards. Many of these functions involve applying liquid chemicals evenly over the surface of opposite sides of the printed circuit boards. Since a horizontal orientation of the printed circuit boards may result in "pooling" of these chemicals, it is desirable to process and transport the printed circuit boards in a vertical orientation.
U.S. Pat. No. 4,427,019 to Eidshun is directed to such an apparatus and is specifically designed for the continuous vertical processing of printed circuit boards. The printed circuit boards are gripped and suspended in a vertical orientation by a hanger that is a component of a conveyor system. The conveyor system transports the printed circuit boards through a plurality of chambers having slotted end portions, each chamber being adapted for a particular processing function.
U.S. Pat. No. 4,739,780 to Czaja et al, incorporated herein by reference, is directed to a conveyorized processor system for transporting vertically oriented printed circuit boards. The system includes a geometrically configured printed circuit board holder. The holder includes a plurality of opposing rubber gripper fingers mounted perpendicularly to each other to form a seating area or pocket. The holder mounts on a conveyor chain or the like. Circuit boards rest vertically in a V-shaped area formed by the gripper fingers for carriage through the processing chambers.
In each of the foregoing systems, each printed circuit board is gripped by the conveyor system at a fixed location on the board and is held by a gripping mechanism in that fixed location for the entire time that it is transported through the processing chamber. Consequently, the areas of the printed circuit board that are gripped may be shielded from the processing chemicals by the gripping components. This may lead to an uneven processing of the printed circuit board in the shielded areas.